Marine caves are peculiar coastal environments
characterized by sharp physical, chemical and hydrodynamic gradients. For
example, light attenuation is responsible for the lack of photosynthetic
production in the inner parts of caves. Thus, the distribution of marine
organisms is related to these selective environmental features, which
allow such caves to be subdivided into distinct ecological zones. On a
small scale, marine caves show high biodiversity and habitat
diversification (both rocky and sandy). For this reason, they can be
considered "miniature natural zoos" where a large variety of marine life,
including deep sea species, is represented. From this point of view, the
study of marine caves may promote a better understanding of the complex
relationships between distribution patterns of organisms and ecological
factors. Moreover, marine caves are particularly relevant in regard to
ongoing marine protection programs of the Italian Government.

Salento Peninsula

Salento is a karstic peninsula located in
southeastern Italy that contains one of the most significant
concentrations of marine caves along the Italian coast (Fig.1) (Onorato et
al., 1999). At present, 53 submerged caves have been described. However,
the geomorphologic uniformity of the coast suggests that many more await
discovery. The well-studied Zinzulusa cave is particularly noteworthy from
a biological perspective. The interior of this cave contains an anchialine
pool, "Il Cocito", inhabited by a stygobiotic fauna including the recently
described endemic sponge Higginsia ciccaresei (Pansini & Pesce,
1998) (Photo 1).

Figure 1: Locations of the most
important marine caves along the Italian coast. The circle indicates the
Salento peninsula.

Photo 1:Higginsia ciccaresei
(Photo by A. Danieli).

Research Activities of the Laboratory of the Marine Biology Station (University
of Lecce)

The high density of marine caves along the
coasts of Salento provides considerable opportunity for biological
investigations. Studies on the ecology of marine caves have been
undertaken to identify environmental issues and to safeguard these marine
ecosystems. Although they have suffered minimal environmental degradation,
in fact, they require careful management because of their fragility. The
Salento, moreover, is affected by a heavy anthropogenic pressure as a
consequence of the date-mussel fishery which leads to desertification of
shallow rocky bottoms (Fanelli et al., 1994). Thus, marine caves are
important sites for preserving the environmental integrity of those areas.A preliminary survey was carried out in the
underwater cave "Grotta delle Corvine" (Belmonte et al., 1999; Denitto et
al., 1999) (Fig. 2; Photo 2). The results displayed a high biodiversity of
sessile fauna (only among sponges, 46 species were recorded) and some
uncommon patterns of colonization of hard substrates (Photo 3; 4; 5a; 5b;
6a; 6b). Also noteworthy is the presence on the soft bottom of a dense
population of the ceriantid Arachnanthus oligopodus (Photo 7),
formerly reported only from a submerged cave near Marseilles, France
(Harmelin et al., 1987). The plankton, still under study, contains many
components of the so-called hyperbenthos (mainly copepods).

Photo 3: Red algae such as
Peyssonellia squamaria and Lithophyllum frondosum are
very abundant within 5 m from the cave mouth.

Photo 4: A rich population
of the yellow anthozoan Leptosammia pruvoti characterizes the
rocky walls at 15-35 m from the entrance.

Photo 5a: A diversified
assemblage of sponges develops on the rocky walls and ceiling of the
cave.

Photo 5b: Closeup view of
the sponge Agelas oroides.

Photo 6a: Serpulid
polychaetes colonize the rock walls of the inner part of the cave
(35-50 m from the entrance).

Photo 6b: Closeup view of
Serpulidae.

Photo 7: A dense population
of the cerianthid Arachnanthus oligopodus on the soft bottom of
the middle part of the cave.

From a morphological viewpoint, submerged caves
of the Salento show a peculiar type of coralligenous speleothem (a complex
biogenic substrate built by calcareous rhodophytes) which hangs from the
ceiling in up to 1.2 m long club stalactites (Photo 8). If is not know if
these speleothems have a rocky core, or they are the result of a
"trickling" organogenous formation.